Pegasus - Robin Mckinley

Because she was a princess, she had a Pegasus.

Princess Sylviianel has always known that on her twelfth birthday she too would be bound to her own Pegasus. All members of the royal family have been thus bound since the Alliance was made almost a thousand years ago; the binding system was created to strengthen the Alliance, because humans and pegasi can only communicate formally, through specially trained Speaker magicians. Sylvi is accustomed to seeing pegasi every day at the palace, but she still finds the idea of her binding very daunting. The official phrase is that your pegasus is your "Excellent Friend." But how can you be friends with someone you can't talk to?

But everything is different for Sylvi and Ebon from the moment they meet at her binding-when they discover they can talk to each other. They form so close a bond that it becomes a threat to the status quo-and possibly to the future safety of their two nations. For some of the magicians believe there is a reason humans and pegasi should not fully understand each other.